EvilRufusKay Posted July 29, 2003 Share Posted July 29, 2003 Hey Guys, I was wondering if I could get some opinions on ignition timing / carb setup for my sbc. I did not put the engine together but this is what I know about it. MSD Ignition box, MSD Dist. Edlebrock (750?) cfm RV/Performance cam (make unknown) possible over bore of .30 or .40 I say this because when I bought the car the kid told me it was .40 over but his knowledge of mechanics is very limited. Unlike my own !! I was wondering how I can tell if the ignition box is working correctly,and what a good start point for ignition timing might be. I have read 16 and 14 BTC but the car seems to like 12 better. Also tips on tuning this old carb. Set the idle low, tune the air adjust screws rich then back off? I tried these things last night and it is running pretty good but a little rough on the low end 1500 - 2500 rpm. Above that very smooth. The exaust seems rich and burns the eyes when sitting in the car at idle. I appreciate any help. Thanks!! Quote Link to comment Share on other sites More sharing options...
Guest DaneL24 Posted September 3, 2003 Share Posted September 3, 2003 Sounds to me like your primaries in the carb are too rich. Just lean out the primaries and leave the secondaries alone...see if that helps. The performance cam could make it run rough in the lower RPM range too...depending on how much lift and duration it has. As far as ignition timing goes...I would just set it at TDC and advance to the point that it pings under high load...then back off the timing so it doesn't ping. Take the car on test runs and after each test...advance the timing ever so slightly. Repeat this again and again, advancing the timing a little more each time. You'll know when it starts pinging and you need to back off (retard) the timing. This method will allow you to run the timing as advanced as possible without harming the motor. But if it runs well at a certain setting, just keep it there. After you find the best setting, you might even want to retard the timing a little more just to be on the safe side. Also, its best to do the timing test with low octane gas in the tank. That way you know you'll be safe from pinging with any octane rating of gas. If you do the test with 93 octane in the tank, set the timing, and then put in some 85, you'll be in trouble. Since high octane gas is ping resistant, thats why you want to use low octane gas while setting the timing. Also, the higher the altitude you live at, the lower of an octane rating you can get away with. Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted September 29, 2003 Share Posted September 29, 2003 I was not aware that octane was related to altitude.. interesting. Quote Link to comment Share on other sites More sharing options...
Guest Nic-Rebel450CA Posted October 27, 2003 Share Posted October 27, 2003 yes, altitude has a bearing on the octane requirements, but it is ever so slight. It is only because of the little bit of difference in oxygen in the air and the air density. as I have pointed out in many posts, your engine has to be pretty significantly modified to need anything but low octane gas. running too high of octane hurts your mileage, power, engine, and wallet. As far as changing the jets (your question in another thread), you should be able to get some leaner jets without knowing the exact cam specs. Knowing the cam specs will help you get the best setup, but it isnt needed to get a better setup. There are also a number of shops that can determine your cam specs without taking it out of the block by measuring the lift and duration at the rocker arm. When adusting the mixture, do the following: First adjust your idle, set it low, and have the mixture screws all the way in. Back them out until the RPMS get as high as they are going to, and then run them back in a 1/4 turn or so. (I have heard of some carbs where this screw is setup the opposite, and is richest when it is all the way in, double check your carb info to be sure) Your carb should have an adjustment for the overal mixture as well. Since that is probably already rich, back it out some and the RPM should start to drop. If the RPMS dont immediately drop, then it is probably way too rich. Once the RPMS start to drop, back it out another 1/4 turn and take it for a spin. If you have a stick shift, shift it from 2nd into 4th and floor it, this is any easy way to check for pinging under heavy load. If you hear pinging, richen the mixture up a little and try again. If there is no pinging, try leaning it just a little more. Just remember the following: Running rich never helps power, you only get power from the gas you burn. Running too lean can destroy your engine! Be careful when leaning out a mixture. Of course, there is no substitute for one of those color meters for checking AFM, you might want to invest in one if you are sticking with a carb. EDIT: HaHa, if you misspell shift the site changes it to "dodo" Quote Link to comment Share on other sites More sharing options...
EvilRufusKay Posted October 27, 2003 Author Share Posted October 27, 2003 I was thinking of getting one of those but like I said before I think I would rather save my money for an EFI set up. I do not think my carb has a set screw for overall AFM just the to screws in the front. If I am correct in my thinking those screws only adjust AMF at idle. I notice rich exaust when backing off the throttle, but it is also present most of the time. Quote Link to comment Share on other sites More sharing options...
Guest Nic-Rebel450CA Posted October 27, 2003 Share Posted October 27, 2003 the overall is normally like a pod thing on one side, the screws in the front are going to be for the idle, yes. if you take some pics of the sides of your carb i can probably get you more info. Quote Link to comment Share on other sites More sharing options...
EvilRufusKay Posted October 27, 2003 Author Share Posted October 27, 2003 I haver a couple of pics of my carb but don't have a web space to post them from. Do you have any suggestions for free hosts? Quote Link to comment Share on other sites More sharing options...
Guest Nic-Rebel450CA Posted October 27, 2003 Share Posted October 27, 2003 You can upload them to your album here, just click on Album, then Your Personal Gallery, then Upload Pic. Quote Link to comment Share on other sites More sharing options...
EvilRufusKay Posted October 27, 2003 Author Share Posted October 27, 2003 The pics are in my album..Thanks for the help. Can you use the album to show the pics in your post with or without a link? Quote Link to comment Share on other sites More sharing options...
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